acclimation: The process by which an organism adapts
to climate changes in the environment.

acid rain: Sulfuric acid in raindrops due to
atmospheric pollution from sulfur dioxide.

advisory: A forecast issued by the National Weather
Service regarding weather conditions that might require caution.

air: The mixture of gases that forms the atmosphere of
the Earth.

air pollution: Substances in the atmosphere that
directly or indirectly causes harm to living things and property.

air pressure: Air has weight. Air pressure is the
weight of the air, or atmosphere, pushing down on Earth. The closer you
are to sea level, the higher the air pressure because there’s that
much air above you. The higher you are, there is less air pressure.
Barometers measure air pressure.

almanac: A calendar with astronomical and weather
data.

altitude: Height expressed above sea level or ground
level.

aridity: The level at which a climate does not receive
enough life-promoting moisture.

atmosphere: The gaseous fluid surrounding a
planet.

aurora: A luminous phenomenon seen in the night sky,
caused by the interaction of solar wind and Earth’s magnetic
field.

Aurora Australis: The aurora, or southern lights, of
the Southern Hemisphere.

Aurora Borealis: The aurora, or northern lights, of
the Northern Hemisphere.

autumn: Season of the year marking the transition from
summer to winter.

Celsius: Zero degrees is the melting point of ice (32
degrees Fahrenheit), while its 100-degrees is the boiling point of water
(212 degrees Fahrenheit). The Celsius scale replaced the Centigrade scale
in 1948.

desertification: The formation or increase of desert
like conditions in a region.

drought: A long period of no rainfall in a region. Droughts
can destroy crops, dry up water supplies, and sometimes lead to widespread
hunger or famine. The lack of moisture in the soil can also cause dust
storms. (See alsoDroughts and Heat Waves.)

dry: very little precipitation or moisture, as in a
dry-climate.

Fahrenheit: A temperature scale in which the melting
of ice is at 32 degrees (0 degrees Celsius), and water boils at 212
degrees (100 degrees Celsius).

flood: a great flowing or overflowing of water, esp.
over land not usually submerged.

Global warming: The theory that the Earth's temperature is growing
warmer. In the future, global warming is expected to have damaging
consequences to human life and the Earth's ecosystems. Many climatologists
believe that increasing concentrations of carbon dioxide and other “greenhouse gasses” in the atmosphere are the cause of global warming.

Green house effect: an atmospheric heating phenomenon,
caused by short-wave solar radiation being readily transmitted inward
through the earth's atmosphere but longer-wavelength heat radiation less
readily transmitted outward, owing to its absorption by atmospheric carbon
dioxide, water vapor, methane, and other gases; thus, the rising level of
carbon dioxide is viewed with concern.

hail: Pellets of ice and snow created within clouds, that
then fall to Earth. Hailstones can sometimes be quite large and can cause
significant damage. The largest hailstone ever recorded in the U.S. was
found in Aurora, Neb., on June 22, 2003. It measured 7 in. in diameter and
18.7 in. in circumference. The costliest U.S. hailstorm took place on July
11, 1990, in Denver, Colorado. The total damage was $625 million.

humidity: The amount of water vapor in the air. Relative
humidity is the amount of water in the air compared to the amount of
water the air can hold at that temperature. When the relative humidity
reaches 100%, the air has reached its dew point. Once the air
reaches this point, the water vapor turns back into water in the form of
rain, snow, clouds or fog.

Hurricane: Major storms with strong winds ranging from 40
m.p.h. to 150 m.p.h. Violent storms occurring in the region of the
Atlantic Ocean are known as hurricanes. When they appear in the Pacific
they are called typhoons. (See alsoHurricane Season.)

ice: The solid phase of water. The volume of ice is
about 10 percent greater than when the ice melts into liquid form.

jet stream: Occurring about 6 to 9 miles above the
ground, the jet stream is a belt of very strong winds.

lightning: Flashes of electrical discharges moving through the
atmosphere during thunderstorms. There are
different types of lightning: forked lightning (a jagged streak), sheet or
streak lighting (a broad flash across the sky), and very rarely as a ball
lightning (an illuminated ball). (See alsoLightning Advice.)

Meteorologist: A person professionally employed in the
study or practice of meteorology.

Meteorology: The study of the atmosphere and all its
phenomenon.

muggy: Calm air that is warm and extremely humid.

overcast: The sky covered by layers of clouds with no
openings.

precipitation: Condensed moisture that falls to the earth as rain,
sleet, snow, frost, or dew.

rain: liquid precipitation in the form of water
droplets.

rainbow: The refraction (bending) of sunlight passing
through raindrops or fog sometimes causes a beautiful arc of colors to
appear in the sky for a brief period. The sun, the arc, and the person
observing it must be aligned just so in order for the rainbow to be
visible.

thunder: The loud noise that follows lightning during a
thunderstorm. You can
estimate how many miles away a storm is by counting the number of seconds
between the flash of lightning and the clap of thunder. Divide the number
of seconds by five to get the distance in miles. The lightning is seen
before the thunder is heard because light travels faster than sound.

tornado: A tornado is a dark funnel-shaped cloud made up of
violently rotating winds that can reach speeds of up to 300 m.p.h. The
diameter of a tornado can vary between a few feet and a mile, and its
track can extend from less than a mile to several hundred miles. (See
also Tornadoes.)

water cycle: The process of water changing from one
state to another and its movement from one place to another. For example,
when it rains, water drops fall to Earth. This water evaporates from the
surface of Earth and enters the atmosphere as water vapor. The water vapor
then condenses into droplets that form clouds.

wind chill: The wind chill temperature indicates how cold
people feel when outside. As the wind increases, it draws heat from the
body, driving down skin temperature and eventually the internal body
temperature. The wind therefore makes it feel much colder. If, for
example, the temperature is 0°F and the wind is blowing at 15 mph, the
wind chill is –19°F. At this wind chill temperature, exposed
skin can freeze in 30 minutes. (See alsoRevised Wind Chill Factor.)

winter: The season of the year marking the transition
from Autumn to Spring.